A zoom lens system includes a first lens unit, a second lens unit, a third lens unit, a fourth lens unit, a fifth lens unit, and a sixth lens unit. In zooming, at least the first lens unit, the second lens unit, and the third lens unit move along an optical axis so that an interval between the first lens unit and the second lens unit at a telephoto limit becomes larger than that at a wide-angle limit, and an interval between the second lens unit and the third lens unit at the telephoto limit becomes narrower than that at the wide-angle limit. An aperture diaphragm is disposed between the second lens unit and the third lens unit. A condition of 18.5